@use 'sass:math';
@use 'is-integer' as *;

/// Generates the values to create a long shadow on text or any other element.
/// Used by the `long-shadow()` mixin, but can also be used on its own as the
/// value for a `text-shadow` or `box-shadow` property.
///
/// @param {Color} $color [hsla(0, 0%, 15%, 0.95)] - The color of the long shadow.
/// @param {Number} $longness [20] - Used to calculate the length of the shadow.
/// Must be a unitless integer greater than 0.
///
/// @return {List} The list of values that can be used by the `text-shadow` or
/// `box-shadow` properties. These values are also used by the `long-shadow()`
/// mixin.
///
/// @access public
/// @group Utilities
/// @require {function} is-integer
/// @see {mixin} long-shadow
///
/// @throw Invalid $longness value error, must be a unitless integer greater
/// than 0.
@function make-long-shadow($color: hsla(0, 0%, 15%, 0.95), $longness: 20) {
  @if not is-integer($longness) or
      not math.is-unitless($longness) or
      $longness <= 0
  {
    @error 'Invalid input for $longness in the [ make-long-shadow() ] ' +
        'function. This value must be a unitless integer greater than 0. ' +
        'It is used by the function to calculate the values for the length ' +
        'of the shadow, most commonly for the [ long-shadow() ] mixin.';
  }

  $val: 0 0 #{$color};

  @for $i from 1 through $longness {
    $val: $val, $i * 1px $i * 1px #{$color};
  }

  @return $val;
}